As is known, in several cases it is necessary to use compressed air in order to operate actuators in machines of the automatic type. Control of the mechanical action of these actuators is usually performed by resorting to pressure regulation valves.
If the need to vary the pressure is continuous and is part of an automatic cycle, it is usual to use electronically controlled proportional electric valves.
Substantially, the operating principle consists in generating a magnetic force, which is proportional to the deviation between the pressure set point and the output pressure detected with an appropriate transducer arranged internally, which is compensated by a return force, which is generated by the selected output pressure and can be varied at will.
These elements, which are usually commercially available and are provided by various manufacturers, have immediate response times, limited hysteresis of the control system, and high sensitivity.
However, if a continuous variation of the pressure of the compressed air is required in order to supply a plurality of automatic actuators which perform different functions and are variously distributed on the machine with considerable distances between the regulation point and the actuator, for example more than 8 meters, conventional solutions are not satisfactory.
Due to the high compressibility of compressed air and to the elasticity of the system, which is generally provided by means of plastic hoses, with consequent continuous changes to the overall volume and to the propagation time, the use of electronically-controlled proportional electric valves, which have immediate response times and in which the pressure transducer for controlling the output pressure is arranged inside them, i.e., at a considerable distance from the point of use, has drawbacks due to the offset between the actual pressure in the two adjustment and utilization points.
In order to prevent this offset from interfering with the correct operation of the actuator, it is necessary to wait for the system to stabilize by introducing a delay time between the regulation command and the command of the actuator, which must be determined experimentally for each actuator, or by varying gradually the set point of the proportional electric valve in order to be certain that the two pressures are equivalent at all times.
The times of the operating cycle of the machine are of course affected negatively by the phenomena described above and by the consequent attenuation methods.
Another solution for reducing this phenomenon might consist in reducing drastically the proportional gain of the regulator arranged inside the proportional electric valve, but this is practically unfeasible due to the limited sensitivity of the regulation system.